Comprehensive and Detailed Explanation From Exact Extract:

High-Temperature Hydrogen Attack (HTHA) is described in API RP 571 and API RP 941 as a damage mechanism where hydrogen reacts with carbides at elevated temperature and pressure, forming methane and causing loss of strength and fissuring.

Prevention is primarily achieved by selecting materials with stable carbides that resist hydrogen attack. Chromium and molybdenum alloying elements:

Form more stable carbides

Reduce susceptibility to methane formation

Extend safe operating limits

Why the other options are incorrect:

Option B may be used in some services but is not the usual prevention method.

Option C is incorrect because RP 941 does not recommend high-nickel alloys as the primary solution.

Option D low-carbon steels are more susceptible, not resistant.

API RP 571 clearly identifies Cr-Mo alloy steels as the standard mitigation approach.

Referenced Documents (Study Basis):

API RP 571 – Section on High-Temperature Hydrogen Attack

API RP 941 – Nelson Curves and Material Selection

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